Figure of bone growth out of a cartilaginous pre-stage (chondral ossification). The ossification starts in the diaphysis (middle shaft) of a long hollow bone of the fetus (primary centre of ossification). During later stages (post-birth), the secondary centres of ossification develop in the epiphysis of the bone. They enlarge and, until the bone stops growing in length, leave open a growth / epiphyseal gap at the transition to the shaft.
